In vitro evaluation of surface topographic changes and nickel release of lingual orthodontic archwires.

The objective of the article is to study surface topographic changes and nickel release in lingual orthodontic archwires in vitro. Stainless steel (SS), nickel-titanium (NiTi) and copper-nickel-titanium (CuNiTi) lingual orthodontic archwires were studied using atomic absorption spectrometry for nickel release after immersion in a saline solution. Surface roughness changes were measured using atomic force microscopy. Differences between groups were analyzed using independent sample t-tests. Statistically significant changes in roughness were seen in all archwires except NiTi. Surface changes were most severe in the CuNiTi alloy. SS archwires released the highest amount of nickel. In conclusion, only roughness changes in CuNiTi archwires seemed to be clinically significant. The amount of nickel released for all archwires tested is below the levels known to cause cell damage.

The effect of constant height bracket placement on marginal ridge levelling using digitized models.

Bracket placement is an important phase of orthodontic treatment. Final compensatory archwire bends or bracket repositioning may be avoided if brackets are accurately positioned at the outset, so as to correctly express their built-in prescription. The purpose of this study was to investigate the levelling of marginal ridges when a bracket placement protocol, with fixed values from the incisal edges and occlusal surfaces, was used on digitized models. A computerized tool, OrthoCAD, was used to predict the end result using virtual set-up software. The appliances used for digital simulation were 3M MBT Victory Series 0.022 inch with a 0.019 x 0.025 inch stainless steel final archwire on 42 digitized models. A paired t-test was used to investigate differences between the means of the pre- (T1) and post- (T2) treatment marginal ridge heights. The results showed that most of the marginal ridge points studied deteriorated during digitized treatment prediction compared with T1. Statistical and clinically significant changes (P < 0.05) were found for upper premolar and lower molar marginal ridge points. Variability in the facial contour of the teeth seemed to play an important role.